The use of computer technology allows substantially instantaneous printing of images. For example, video cameras or scanners may be used to capture a color image on a computer. The image may then be printed onto substrates from the computer by any suitable printing means capable of printing in multiple colors, including mechanical thermal printers, ink jet printers and electrophotographic or electrostatic printers. These printing technologies are widely practiced and well understood. The methods for making full color inks and toners are also well documented (L. B. Schein. “Electrophotography and Development Physics”: Springer Series in Electrophysics 14; Springer-Verlag, 1988). The substrates for these conventional applications, however, are limited to those that the printers can handle, invariably, smooth metal, plastic or papers of limited thickness.
Other techniques are well known in the art for printing onto clothing, other textile materials, and other objects including silk screening, digitally produced sublimation transfers, and mechanically bonded thermal transfers. For example, a process of thermal transfers, wherein the ink mechanically bonds to the substrate, is described in Hare, U.S. Pat. No. 4,773,953. The resulting mechanical image, as transferred, is a surface bonded image with a substantial ‘hand’ or a raised, plastic-like feel to the touch and relatively poor dimensional stability. In addition, the entire sheet is transferred with the non-imaged area as well, but without involving any chemical bonding or cross-linking process (U.S. Pat. Nos. 6,103,042, 5,978,077, 5,985,503, 4,066,802, 4,064,285, 5,981,077, 6,017,636, DE-A 27,27,223, EP-A 466,503, JP-A 63296982, WO 90/13063). It is also known through U.S. Pat. Nos. 5,785,790, 5,679,198, and 5,612,119 a screen printed support sheet, which may have an embedded layer of microspheres, printed with one or more layers of two-component colors based on polyester resin and an isocyanate hardener. The microspheres may have a reflective layer to allow the transferred image printed thereon to reflect light. If more than one color layer is printed onto the microspheres, then a two-component extender or glue that contains polyester is covered on top of each color layer. On top of the extender layer or single-color layer is applied a powder of polyester or polyamide elastomer, which is then fused into the color layer. Instead of screen printing, a color copier using a two-component toner may be used for applying the color coatings. The color coatings are subsequently covered with this elastomeric powder, which is then fused into the layer prior to transfer.
Conventional heat-melt thermal printing uses primarily non-active wax or wax-like materials such as hydrocarbon wax, carnauba wax, ester wax, paraffin wax, hot-melt resin, thermoplastic, or polymeric materials, etc. as heat-melt material. The resulting image has poor permanency since the conventional wax materials are not chemically bonded or otherwise permanently grafted to the substrate, but are temporarily and loosely bound to the final substrate by the melting of wax materials during the transfer process. The resulting image is not durable, with the wax materials being washed away during laundering of textile substrates on which the image is transferred, along with the dyes or colorants that form the image in the thermal ink layer.
Cooper, et al. in U.S. Pat. No. 4,216,283 teaches a xerographic process of dry image transfer with adhesive toner materials. The electrostatic image is developed with a low melting temperature dry toner composition containing a thermoplastic agent to give an image that is pressure-transferred to a receptor surface. This process uses both low melting temperature plasticizer and foamable microspheres to treat toner material in order to achieve the adhesiveness between toner and substrate. However, it does not chemically bind the toner to the final substrate and thus has poor image permanency.
The natural tendency of cotton fiber to absorb inks causes an image to lose its resolution and become distorted. Liquid inks, other than sublimation inks, wick, or are absorbed by, cotton or other absorbent substrates, resulting in printed designs of inferior visual quality, since the printed colors are not properly registered on the substrate. This is especially true when aqueous based ink paste is used for coating and fixing purposes as disclosed in U.S. Pat. No. 5,607,482. The substrates can be surface pre-coated or treated to improve the quality of images transferred onto substrates having a cotton component or other absorbent component with materials such as the coatings described in DeVries et al., U.S. Pat. No. 4,021,591. Application of polymer surface coating materials to the substrate allows the surface coating material to bond the ink layer to the substrate, reducing the absorbency of the ink by the cotton and improving the image quality. However, the gross surface coating on the substrate extends from the margins of the image after the image is applied to the substrate, and can be seen with the naked eye and adds hand to the fabric. Again the excess surface coating reduces the aesthetic quality of the printed image on the substrate. Furthermore, the surface coating tends to turn yellow with age, which is undesirable on white and other light colored substrates. Yellowing is accelerated with laundering, exposure to heat, chemicals, sunlight, or other harsh conditions. A method described in Hale, et al., U.S. Pat. No. 5,431,501, reduces the hand by printing a surface preparation material over the entire image, on the intermediate substrate, but not beyond the boundaries of the image. The image is then transferred from the medium to the final substrate by applying heat and pressure such that the surface preparation material permanently grafts the ink solids to the substrate.
The use of heat by electrographic devices such as laser printers and photocopiers presents the problem recognized in Hale U.S. Pat. Nos. 5,246,518, 5,248,363 and 5,302,223 of printing heat activated inks in a non-activated form by means of such devices. Laser printers and photocopiers in common use employ relatively high temperature fuser devices to thermally fuse or bind the ink to the substrate, since these devices anticipate that the image will be permanently bonded to the substrate which is printed by the device, and do not anticipate a subsequent thermal transfer of the printed image from the substrate.
Hale, et al., U.S. Pat. Nos. 5,555,813 and 5,590,600, describe the process of producing full color images electrostatically using sublimation toner. The images are printed onto a paper substrate and then heat transferred onto a polyester coated substrate at about 400° F. In sublimation transfer printing, solid dyes change to a gas at about 400° F., and have a high affinity for polyester at the activation temperature. Once the gasification bonding takes place, the ink is printed with substantial permanency, and is highly resistant to fading caused by environmental exposure, such as to light, or exposure to certain common chemical processes, such as cleaners or laundry products. However, these applications yield excellent results only when a synthetic material substrate is used, these dyes have a limited affinity for other materials, such as natural fabrics like cotton and wool.
In order to reduce the hand of a resin-formed image on fabric, a method described by Takama, U.S. Pat. No. 5,822,671, involves printing a resin-formed image onto a recording medium, such as cloth, followed by treatment of the recording medium with a plasticizer solution. The plasticizer penetrates between the resin molecules thereby imparting pliability to the fabric. Thompson, U.S. Pat. No. 6,143,454, discloses a dye sublimation toner using high molecular weight, cross-linked polymer resins that neither melt nor become tacky at temperatures needed to sublimate disperse dyes. In this way, it is reported that the toner itself does not transfer from the intermediate sheet to the final polyester substrate except the disperse dye component in the toner. In addition, this type of high molecular weight cross-linked resin may not fuse sufficiently to the intermediate sheet since the resin does not melt at the fuser roller temperature that is necessarily lower than sublimation temperature.
Gorondy, U.S. Pat. Nos. 4,421,515 and 4,421,517, describes a three-transfer step process of by using magnetic imaging toner containing a sublimation dye component. An image is generated by developing and transferring onto a continuous belt of thermally stable material; then such an image is transferred and laminated between two polymer films of polyester, polyamide, or polyvinyl chloride with heat and pressure. The lamination is then placed in contact with a fabric and heat is applied to subsequently sublimate and transfer the image to the polyester, polyamide, or the similar fabric.
Polyester resin materials have been used for various coating applications, as disclosed in U.S. Pat. No. 6,068,797. Recently polyester resins have been employed in toners in order to allow fusing at lower temperatures than traditional styrene-acrylic systems and since they have high levels of negative chargeability. Polyester resins also have a good resistance to plasticizers so that, for example, images placed in a polyvinyl chloride sleeve do not become blurred and indistinct. For example, DeMajo, et al. U.S. Pat. No. 5,112,715, and Bayley, et al. U.S. Pat. No. 5,486,444, describe the preparation of cross-linked polyesters that melt and are permanently fixed to the support medium. Matsumura, et al. U.S. Pat. No. 4,968,575, describe the preparation of rosin-containing polyesters for toners. However, it teaches the reduction of hydroxyl value by blocking terminal hydroxyl groups of polyester polyol molecules with a rosin compound in order to achieve desirable charging behavior of the toner. U.S. Pat. No. 6,103,041 teaches a method of digitally printing ink having components, whose functional groups are capable of reacting with active hydrogen, in an un-reacted state onto a substrate. The image is subsequently transferred or permanently fixed on the substrate by the application of heat and pressure, which activates the ink, and bonds the colorant to the substrate. The reactive compounds may be blocked with blocking agents, which are removed by the application of heat or other energy during activation of the ink. However, this method requires preparing a wax thermal ribbon comprising liquefiable hot-melt ink.
These techniques all suffer various drawbacks such as requiring specially coated substrates, producing images that suffer from excessive “hand”, relatively low resolution, relatively low imaging speed, poor image quality, vibrancy, and/or permanency when the image is transferred to a fibrous natural material such as cotton or wool. Accordingly there remains a need for a digital printing process using inks or toners, and methods for making same, that provides for example, satisfactory electrical and physical properties of the toners during the printing of an image to an intermediate substrate before permanently affixing the image onto a fibrous natural or synthetic substrate with good quality, vibrancy, permanency and little ‘hand’.